1. Field of the Invention
The field of art to which this invention pertains is to regeneration and stabilization of phosphorus-vanadium-oxygen complex catalysts and, in particular, the stabilization of catalysts used for the production of oxygenated products including aldehydes, ketones, acids, anhydrides, and mixtures thereof from hydrocarbon feedstocks. In a specified instance, the claimed regeneration and stabilization procedure is advantageously used on a catalyst used for the production of maleic anhydride from a specified feedstock, namely, normal butane in air. Pertinent U.S. Patent and Trademark Office classifications include Class 260, subclass 346.8.
2. Background of the Invention
In general, catalysts proposed for the oxidation of butane, other C.sub.4 hydrocarbons, and benzene to maleic anhydride have been based upon vanadium and phosphorus. In U.S. Pat. No. 3,293,268, it is disclosed that the oxidation of butane to maleic anhydride can be performed in the presence of a phosphorus-vanadium-oxygen-containing complex catalyst. Though this catalyst is capable of oxidizing butane, it does not give sufficiently high yields of maleic anhydride. Yields of maleic anhydride of only 30 to 50 weight percent are reported. Various activators, stabilizers, and promoters have been disclosed in the prior art to improve the yields of maleic anhydride. References include U.S. Pat. Nos. 3,867,411; 3,832,359; 3,888,886; 4,002,650; 4,147,661; 4,149,992; 4,151,116; 4,152,338; 4,152,339; 4,081,460; 4,043,943; 4,154,703; and British Application No. 2,019,839A. While the aforementioned prior art tends to bring about some improvement in the performance of the phosphorus-vanadium catalyst, there remains much room for improvement, particularly from the standpoint of high conversion, yield, and catalyst life. U.S. Pat. No. 4,081,460 relates to molybdenum-vanadium catalysts which are regenerated by the addition of phosphorus. Other references of interest include U.S. Pat. Nos. 4,002,174; 4,094,816; 4,089,807; 3,296,282; 3,474,041; and British Pat. No. 1,464,198.